Question

Two children push on opposite sides of a door during play. both push horizontally and perpendicular to the door. one child pushes with a force of 185 n at a distance of 0.500 m from the hinges, and the second pushes at a distance of 0.450 m. what force (in n) must the second exert to keep the door from moving? assume friction is negligible.

Answer 1

If door is not rotating about its hinge then its net torque due to both child must be zero

Torque is defined as product of force and its perpendicular distance from the hinge.

so for both child we can say

`T_1 = T_2`

`r_1* F_1 = r_2* F_2`

`0.5 * 185 = 0.45 * F`

`F_2 = (0.5 * 185)/(0.45)`

`F_2 = 205.5 N`

so 2nd boy must have to apply F = 205.5 N